A cutback asphalt is manufactured by blending asphalt with a volatile diluent such as naphtha or mineral spirits. The diluent reduces the viscosity of the asphalt so that the cutback asphalt can be transported and used at lower temperatures. After the cutback asphalt is applied, the diluent evaporates to increase the viscosity of the product. Cutback asphalts are used for paving and other applications.
After manufacture, the cutback asphalt is usually held in a storage tank, and then dispensed into a tanker truck at a loading station for transport to the customer. During the dispensing, vapors of the volatile diluent are emitted from the cutback asphalt. The vapors create an environmental problem if too many vapors escape into the atmosphere.
To address this problem, a system could be installed to return the vapors to the storage tank. This system has not proven to be effective for recovering vapors at a cutback asphalt loading station. The system also requires special equipment which increases the cost and complexity of the dispensing operation.
Vapor recovery methods disclosed in previous patents also do not adequately address this problem. For example, U.S. Pat. No. 5,591,244 discloses the recovery of asphalt vapors from a roofing asphalt supply truck as the asphalt is pumped from the truck to the roof The vapors are recovered and filtered. There is no condensation involved, and no return of any substance to the asphalt material.
U.S. Pat. No. 4,515,189 discloses vapor recovery during the filling of rail tank cars with molten sulfur. There is no disclosure of asphalt vapors, and no disclosure of returning condensed vapors to the tank.
In view of the shortcomings of the previous vapor recovery methods, it would be desirable to provide a method for recovering vapors during the dispensing of a bituminous product such as cutback asphalt into a tank, where the method is relatively simple and inexpensive, and where the method is very efficient in recovering the vapors.